Cosplay is definitely a huge part of anime conventions. In addition to all the hall costumes, there are numerous cosplay events and costume contests. It's always fun to dress up as your favorite character and have your picture taken. Here's some advice about cosplaying at an anime convention.

Do I need to wear a costume to the convention?
Not at all. You can definitely enjoy a convention without dressing up.

What do I do if I want to take a picture of a cosplayer?
Simply ask if you can take their picture. Almost always they will say yes - cosplayers love to have their picture taken because it shows that people like their costume. However, please be respectful if they say no. They may be in a rush to meet someone, go to a panel or judging, or something else. Also, don't ask if someone is eating. Chances are they may not have their whole costume on and they want to take a break and relax for a few minutes.

When you take the picture, take a second to make sure that you aren't blocking the flow of traffic. Also make sure that you aren't in front of a big window or anything that might cause glare and ruin your picture. After you take the picture it's nice to thank the cosplayer.

I want to wear my Star Trek/My Little Pony/Batman/Avatar/Doctor Who/Harry Potter/Original Character costume to an anime con, is that okay?
I'm of the mindset that you can wear whatever you want to an anime convention, including costumes of Western origin. When you think about it, we're all just nerds in costume, so what's the big deal if you want to wear something that's not Japanese? Don't worry if some people make a big deal about it. Wear whatever you want.

However, most anime convention costume contests require that your character be of Japanese origin, so be sure to check the rules before entering.

I can't make a costume to save my life! Is it okay if I buy one online?
Absolutely. Not everyone has the time to sew a costume, or their skills may not be good enough yet to make what they want. It is not a bad thing at all to buy your costume online. Again, don't worry if people make a big deal about it. Cosplaying is about having fun.

However, do not say you made the costume when you actually bought it, and whatever you do, don't enter it in any craftsmanship judging. That is cheating.

Can I buy a costume in the dealers room?
Maybe. It depends on the convention and what dealers they have. You have a better chance of finding costumes at a larger convention than a smaller one though. Check the dealers room listing for the specific convention you're attending to see if there are any costume vendors.

Should I bring things like a needle and thread with me?
That and more. Every cosplayer should pack a "Cosplay Repair Kit" whenever they are going to a con. See the article What to Pack in a Cosplay Repair Kit for a list of suggestions.

I don't have a hotel room. How can I change in and out of my costume, and what do I do with it when I'm not wearing it?
That depends on a few things. If you have a car at the convention, you can store your costume in there when you're not using it. Also, if you have a friend with a hotel room, ask (before the con) if you can use it to change and store your costume when you're not wearing it. If neither of those options are available, I recommend wearing a simple costume that can easily be worn all day without needing to change, or doesn't take up a lot of room so you can put it in bag when you're done.

What is a masquerade? What is a hall costume contest?
A masquerade is a convention's costume contest that involves going on stage, showing off your costume, and in most cases doing a short performance. Entries are judged on craftsmanship and performance. Before going on stage, either earlier in the day or the previous day, you have the option of having your costume judged for craftsmanship. There the judges will look at your costume up close and you tell them how you made your costumes. Performance judges will watch your skit as you perform and judge on what they see.

Hall costume contests are judged on craftsmanship only. These are usually done on Friday and/or Saturday during a convention. There is no onstage performance, but sometimes you have the option of walking in a fashion show during the masquerade. Winners are usually announced after the skits at the masquerade have performed.

If I wear a costume to the convention, am I automatically in the contests?
No, you have to sign up for them (see next question). Some conventions have ribbons that staff members give out to costumes they like, but that is different from entering contests and are just for fun.

How do I enter the costume contest?
Even if you only have a slight interest in entering, check out the rules for the contest online as soon as you can to see what they are. The rules vary from convention to convention, so make sure you read them thoroughly. Take note of any starting dates and deadlines for signups. Big conventions can fill up quickly, but often smaller conventions still take entries at the convention.

What is Cosplay Chess? Dating Game? Court Case?
Cosplay Chess, Cosplay Dating Game, and Cosplay Court Case are various types of cosplay events that anime conventions have. These feature cosplayers acting in character and interacting with characters of different series.

Cosplay Chess is a form of human cosplay, where the characters are formed into two teams, which are controlled by two players, usually two more characters. When a piece takes another piece out, the others move aside and they "battle" on stage. It's very entertaining to see all the different characters from many different series interact with one another.

Cosplay Dating Game is based on the game show The Dating Game. The contestant must choose between three bachelors or bachelorettes, however there is a curtain between them, so they don't know who they will be picking. They ask questions to the contestants, and then pick the one they like best. There is often an 18+ game done as well, which features yaoi and yuri pairings.

Cosplay Court Case puts a character on trial for a crime. There is a judge, prosecutor, lawyer, and witnesses - all cosplayers, usually from different series.